Siren



FIG. 1 is a front, top, right side perspective view of a siren showing our new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a right side view thereof; and,

FIG. 7 is a left side view thereof.

The broken lines in the drawings illustrate portions of the siren that form no part of the claimed design. 

CLAIM The ornamental design for a siren, as shown and described. 